[llvm] [WIP] Optimize S_MOV frame index elimination support (PR #101322)

[Matt Arsenault via llvm-commits]

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@@ -8966,10 +8966,10 @@ MachineInstrBuilder SIInstrInfo::getAddNoCarry(MachineBasicBlock &MBB,
                              : RS.scavengeRegisterBackwards(
                                    *RI.getBoolRC(), I, /* RestoreAfter */ false,
                                    0, /* AllowSpill */ false);
-
-  // TODO: Users need to deal with this.
   if (!UnusedCarry.isValid())
-    return MachineInstrBuilder();
+    // We are using the mad_u32_u24 primarily as an add with no carry out
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arsenm wrote:

Braces. But also need to rename this, since it's not valid in the general case. 

https://github.com/llvm/llvm-project/pull/101322